Adhesive of epoxy acrylate, non-unsaturated resin and bis(methacryloylethyl) hydrogen phosphate

ABSTRACT

An insulating adhesive film and an anisotropically electroconductive adhesive film satisfying low-temperature curability, high adhesion and high reliability are provided. An anisotropically electroconductive adhesive film of the present invention is so configured that electroconductive particles  7  are dispersed in an insulating adhesive resin  6 , comprising as main components: a radical polymerizable resin component having an unsaturated double bond; a resin component having no unsaturated double bond; a phosphoric acid-containing resin component; and a radical polymerization initiator.

This is a Continuation of application Ser. No. 11/514,192 filed Sep. 1,2006, which in turn is a Continuation of application Ser. No. 10/844,307filed May 12, 2004, which in turn is a Continuation of application Ser.No. 09/631,278 filed Aug. 3, 2000, all now abandoned. The disclosure ofthe prior applications is hereby incorporated by reference herein in itsentirety.

BACKGROUND

1. Field of the Invention

The present invention relates to an insulating adhesive and ananisotropically electroconductive adhesive for use in, for example,establishing electric connections between circuit boards. Moreparticularly, it relates to an insulating adhesive and ananisotropically electroconductive adhesive curable at low temperatures.

2. Description of the Related Art

In recent years, as countermeasures against the miniaturization ofportable remote terminals such as portable telephones, and a crack in aliquid crystal cell or glass, there has been extensively examined thepractical utilization of a so-called “plastic film liquid crystal”obtained by replacing the glass of the liquid crystal cell with plastic.

Conventionally, the connection between a liquid crystal panel and acircuit component such as a TCP (Tape Carrier Package) has beenaccomplished by solder, an anisotropically electroconductive adhesivefilm, heat seal, or the like. However, a thermosetting anisotropicallyelectroconductive adhesive film has been mainstream in response to thetrend toward a smaller pitch and a narrower frame, and from theviewpoints of high adhesion and high reliability. Thus, the plastic filmliquid crystal is also required to be connected by the anisotropicallyelectroconductive adhesive film.

The anisotropically electroconductive adhesive film is originallydesigned under the assumption that the connection between glass and TCP,or the like is established by compression bonding connection at hightemperatures and high pressures, for a short time. In a common case, theconnection is established, for example, at a temperature of 170° C. forabout 20 seconds. Even in the case for a low-temperature connection, itis established at a temperature of 150° C. for around 20 seconds.

However, the plastic film liquid crystal which is a material to bejoined is manufactured by laminating an organic material of a protectivelayer or the like on mainly polyether sulphone or polycarbonate.Therefore, at the compression bonding temperatures thereof, the film mayundergo thermal deformation which will not occur with glass, or cracksoccur in ITO (Indium Tin Oxide) electrodes, thereby causing a displayfailure.

For these reasons, the anisotropically electroconductive adhesive filmfor connecting the plastic film liquid crystal is required to have thecharacteristics of establishing the connection at 140° C. or less, andunder low pressures. However, in actuality, among the existinganisotropically electroconductive adhesive films, there is almost no onewhich is connectable at 140° C. or less, and even the one connectable at140° C. or less has a low reliability.

Heretofore, the thermosetting anisotropically electroconductive adhesivefilms which can provide high reliability include various epoxy resins asmain components, and there have been dominant the ones obtained byadding a so-called latent curing agent prepared by micro-capsulating orblocking an amine-based or imidazole-based curing agent, Lewis acid, orother curing agent thereto, and processing and forming the mixture intoa film.

Alternatively, there are also other films obtained by adding variousresins such as thermosetting elastomers and thermoplastic elastomers,thermosetting resins, thermoplastic resins, tackifiers, fillers, andcoupling agents thereto for the purpose of improving variouscharacteristics such as adhesion, moisture resistance, and stickiness.

However, for the conventional anisotropically electroconductive adhesivefilms using such curing agents, since a compression bonding temperatureof 150° C. or more is required for breaking or melting of themicrocapsules, or for dissociation of the blocking agents, the foregoingrequirements cannot be satisfied. Whereas, for the curing agentsconnectable at 150° C. or less, since the usable time length of theanisotropically electroconductive adhesive film (film life) is short, itis difficult to use the film in actual manufacturing thereof.

On the other hand, as the anisotropically electroconductive adhesivefilms which do not contain epoxy resins as main components, there isproposed one of the radical polymerization type obtained by effectingpolymerization with an unsaturated bond catalyst (Japanese PatentLaid-Open Publication No. Sho 61-276873) by the applicant of the presentinvention, and the like. However, there has not been yet developed anyanisotropically electroconductive adhesive film which satisfies therequirements of low-temperature curability, high adhesion, highreliability, and the like.

SUMMARY

The present invention has been achieved for solving such problems in theprior art. It is therefore an object of the present invention to providean insulating adhesive film and an anisotropically electroconductiveadhesive film which satisfy requirements of low-temperature curability,high adhesion, and high reliability.

The present inventors have conducted an intensive study thereon in orderto solve the foregoing problems. As a result, they have found thefollowing fact. That is, an adhesive which is curable at lowtemperatures, and has high adhesion and reliability can be obtained bymixing a radical polymerizable resin component having an unsaturateddouble bond, a resin component having no unsaturated double bond, and aphosphoric acid-containing resin component. Thus, they have completedthe present invention.

A first aspect of the present invention achieved based on such adiscovery pertains to a low-temperature setting adhesive characterizedby containing as main components, a radical polymerizable resincomponent having an unsaturated double bond, a resin component having nounsaturated double bond, a phosphoric acid-containing resin component,and a radical polymerization initiator.

In accordance with a second aspect of the present invention, it is alsoeffective that a phosphate-based coupling agent is further mixed thereinin the first aspect of the present invention.

Further, in accordance with a third aspect of the present invention, itis also effective that the phosphoric acid-containing resin componenthas a radical polymerizable reactive group of the present invention.

Whereas, a fourth aspect of the present invention pertains to ananisotropically electroconductive adhesive characterized in thatelectroconductive particles are dispersed in the low-temperature settingadhesive according to the present invention.

In accordance with a fifth aspect of the present invention, it is alsoeffective that the electroconductive particle comprises a resin particlewhich is deformed when applied with pressure as a nucleus, and anelectroconductive metal thin layer provided on a surface layer portionthereof according to the present invention.

Further, in accordance with a sixth aspect of the present invention, itis also effective that an insulating layer is provided on the metal thinlayer of the electroconductive particle of the present invention.

On the other hand, a seventh aspect of the present invention pertains toan insulating adhesive film characterized by including a peeling sheet,and the above mentioned low-temperature setting adhesive, the adhesivebeing provided on the peeling sheet by coating and drying.

An eighth aspect of the present invention pertains to an anisotropicallyelectroconductive adhesive film characterized by including a peelingsheet, and the above mentioned anisotropically electroconductiveadhesive, the adhesive being provided on the peeling sheet by coatingand drying.

In the present invention having the foregoing structure, the highadhesion based on the large polarity of the phosphoric acid can beobtained by the reaction between the radical polymerizable resincomponent having an unsaturated double bond and the phosphoricacid-containing resin component upon thermo compression bonding.

Consequently, according to the present invention, even when curing iseffected at low temperatures, a desired initial adhesion force can beobtained, thereby ensuring the connection between electrodes whilemaintaining the deformed state thereof during compression bonding.Therefore, it becomes possible to improve the continuity resistance andthe continuity reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1( a) is a view illustrating the configuration showing the stateprior to the thermo compression bonding of a preferred embodiment of ananisotropically electroconductive adhesive film in accordance with thepresent invention; and

FIG. 1( b) is a view illustrating the configuration showing the stateposterior to the thermo compression bonding of the preferred embodimentof an anisotropically electroconductive adhesive film in accordance withthe present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Below, preferred embodiments of the present invention will be describedin details with reference to the drawings.

The present invention is applicable for both of the anisotropicallyelectroconductive adhesive having electroconductive particles and theinsulating adhesive having no electroconductive particle. Further,either liquid or film-like adhesive is acceptable. In each embodiment ofthe present invention, a description will be given to a film-likeanisotropically electroconductive adhesive as an example.

Referring now to FIGS. 1( a) and 1(b), an anisotropicallyelectroconductive adhesive film 1 of the present invention is used forthe connection of ITO electrodes 3 formed on a resin film 2 withterminals 5 of a circuit board 4 such as the TCP or FPC (FlexiblePrinted Circuit), or connection thereof with bumps formed on an LSI chipnot shown. It is so configured that electroconductive particles 7 aredispersed in a film-like insulating adhesive resin 6 formed on a peelingsheet 8.

In the present invention, the insulating adhesive resin 6 contains, asmain components, a radical polymerizable resin component having anunsaturated double bond, a resin component having no unsaturated doublebond, a phosphoric acid-containing resin component, and a radicalpolymerization initiator.

Here, examples of the radical polymerizable resin component having anunsaturated double bond include (meth)acrylate resins each having atleast one or more (meth)acryloyl groups in one molecule and modifiedproducts thereof, unsaturated polyester diallyl phthalate resins, vinylester resins, bismaleimide resins, and the like, and modified productsthereof, and various monomers for viscosity adjustment.

Out of these, the cured product of epoxy acrylate represented by thefollowing chemical formula is particularly preferred in terms ofchemical resistance, toughness, and adhesion.

wherein n is from 0 to 20.

Examples of the resin component having no unsaturated double bondinclude phenoxy resins and modified products thereof, urethane resinsand modified products thereof, acrylic rubbers and modified productsthereof, polyvinyl butyral and polyvinyl acetal, and modified productsthereof, cellulose derivatives and modified products thereof, polyolresins and modified products thereof, rubber-like resins such aspolystyrene-polyisoprene-polystyrene (SIS),polystyrene-polybutadiene-polystyrene (SBS),polystyrene-poly(ethylene-butylene)-polystyrene (SEBS), andpolystyrene-poly(ethylene-propylene)-polystyrene (SEPS), and modifiedproducts thereof.

Out of these, the phenoxy resin represented by the following chemicalformula is particularly preferred in terms of chemical resistance andtoughness.

wherein n is from 1 to 50.

On the other hand, examples of the phosphoric acid-containing resincomponent include phosphoric acid-containing (meth)acrylate andphosphorus-containing polyester resins.

Out of these, the one having a radical polymerizable reactive group ispreferably used from the viewpoint of improving the heat resistance,chemical resistance, and the like.

For example, the phosphoric acid acrylate (acryloyloxy ester-ashedphosphate) represented by the following chemical formula can bepreferably used.

[where n is 0 to 1 in terms of a mean value, and a and b are about 1.5in terms of a mean value.]

Further, as the radical polymerization initiator, in addition to organicperoxides represented by the following chemical formula:

a light initiator can also be used.

Further, a curing promoter, a supplement accelerator, and apolymerization inhibitor can also appropriately be added to theinitiators. Furthermore, latency can also be imparted to the radicalpolymerization initiators and the like by capsulation or blockingthereof.

Still further, various coupling agents can also be added to theinsulating adhesive resin 6 of the present invention.

For example, the vinylsilane coupling agent represented by the followingchemical formula:

and phosphate-based coupling agents can be preferably used.

In particular, the phosphate-based coupling agents can be preferablyused from the viewpoint of improving the adhesion.

A typical phosphate-based coupling agent isisopropyltris(dioctylpyrophosphate) titanate (KR38S manufactured byAjinomoto Co., Inc.).

In the present invention, for more effectively attaining the foregoingobject, the mixing ratio of a radical polymerizable resin componenthaving an unsaturated double bond, a resin component having nounsaturated double bond, and a phosphoric acid-containing resincomponent relative to the insulating adhesive resin 6 is preferably 15to 85% by weight for the radical polymerizable resin component having anunsaturated double bond, 30 to 90% by weight for the resin componenthaving no unsaturated double bond, and 0.01 to 20% by weight for thephosphoric acid-containing resin component. It is more preferably 30 to70% by weight for the radical polymerizable resin component having anunsaturated double bond, 30 to 80% by weight for the resin componenthaving no unsaturated double bond, and 0.05 to 10% by weight for thephosphoric acid-containing resin component.

On the other hand, in the present invention, as the peeling sheet 8, theone made of a fluorine-containing resin such as polytetrafluoroethyleneresin (PTFE), or the one made of a non-silicone-containing material(ex., polypropylene) is preferably used from the viewpoint offacilitating the peeling of the peeling sheet 8 from the adhesive film,and from the viewpoint of allowing the characteristics (adhesion,moisture resistance, and the like) inherent in the adhesive to besufficiently exhibited.

On the other hand, in the present invention, as the electroconductiveparticles 7, there are also used metal particles, and the one obtainedby providing a metal thin layer having oxidation resistance such as gold(Au) plate on the surface of the metal particle. However, from theviewpoint of ensuring good electric connection, there is preferably usedthe one including resin particles which will be deformed under pressureas a nucleus, and an electroconductive metal thin layer provided on thesurface layer portion thereof.

Further, from the viewpoint of ensuring the insulation properties amongthe electroconductive particles 7, there is preferably used the oneobtained by covering the surface of the metal thin layer of theelectroconductive particle 7 with an insulating layer.

Further, the low-temperature setting adhesive of the present inventionand the anisotropically electroconductive adhesive film using the samecan be manufactured by a conventional method.

Namely, electroconductive particles are dispersed in a binder solutionprepared by dissolving the radical polymerizable resin, and the like inan appropriate solvent. The resulting paste is applied onto the peelingsheet, and the solvent is then vaporized by heating or the like,resulting in the objective anisotropically electroconductive adhesivefilm.

EXAMPLES

Below, examples of the anisotropically electroconductive adhesive filmin accordance with the present invention will be described in detailstogether with comparative examples.

Example 1

A solution obtained by mixing respective components at the followingratio was applied onto a PTFE film with a thickness of 50 μm. Thesolvent was then vaporized so that the residual solvent was in an amountof 1% or less to obtain an anisotropically electroconductive adhesivefilm with a thickness of 15 μm.

Incidentally, each component in a solid state out of the followingresins was mixed therein while being appropriately dissolved by asolvent, methyl ethyl ketone (MEK).

Liquid epoxy acrylate (manufactured by Kyoeisya Chemical Co., Ltd.,3002A) 25 wt %

Solid epoxy acrylate (manufactured by Showa Highpolymer Co., Ltd., −60)25 wt %

Phenoxy resin (manufactured by Tohto Kasei Co., Ltd., YP50) 40 wt %

Phosphoric acid acrylate (manufactured by Nippon Kayaku Co., Ltd., PM2)4 wt %

Vinylsilane coupling agent (peroxyketal manufactured by Nippon Oil &Fats Corp., Perhexa 3M) 3 wt %.

Electroconductive particle (manufactured by Sony Chemicals Corp.,Ni/Au-plated acrylic resin particle) 3 wt %

TABLE 1 Composition ratio of Examples and Comparative ExamplesPhosphate- Phosphoric acid Vinylsilane based Organic Epoxy Phenoxyacrylate coupling coupling peroxide Electro- acrylate resin RDX agentagent Perhexa conductive 3002A VR-60 YP50 PM2 63182 A172 KR38S 3Mparticle Example 1 25 25 40 3 — 1 — 3 3 Example 2 25 25 40 — 3 1 — 3 3Example 3 25 25 40 0.1 — 1 — 3 3 Comparative — 25 20 73 — 1 — 3 3Example 1 Example 4 25 25 40 3 — — 1 3 3 Comparative 25 25 43 — — 1 — 33 Example 2

Example 2

An anisotropically electroconductive adhesive film was manufactured inthe same manner as in Example 1, except that the amount of a differenttype of phosphoric acid acrylate (manufactured by Daicel ChemicalIndustries, Ltd., RDX63182) to be added was 3% by weight.

Example 3

An anisotropically electroconductive adhesive film was manufactured inthe same manner as in Example 1, except that the amount of phosphoricacid acrylate (manufactured by Nippon Kayaku Co., Ltd., PM2) to be addedwas 0.1% by weight.

Example 4

An anisotropically electroconductive adhesive film was manufactured inthe same manner as in Example 1, except that the phosphate-basedcoupling agent (manufactured by Ajinomoto Co., Inc., KR38S) was added inan amount of 1% by weight in place of the vinylsilane coupling agent(manufactured by Nippon Oil & Fats Corp., Perhexa 3M) as the couplingagent.

Comparative Example 1

An anisotropically electroconductive adhesive film was manufactured inthe same manner as in Example 1, except that epoxy acrylate was notadded, the amount of phenoxy resin to be added was 20% by weight, andthe amount of phosphoric acid acrylate to be added was 73% by weight.

Comparative Example 2

An anisotropically electroconductive adhesive film was manufactured inthe same manner as in Example 1, except that the amount of phenoxy resinto be added was 43% by weight, and phosphoric acid acrylate was notadded.

TABLE 2 Evaluation results of Examples and Comparative Examples Adhesivestrength (gf/cm) Continuity resistance (Ω) 60° C. 95% 60° C. 95% Initialafter 500 hr Initial after 500 hr Example 1 865 780 9.6 10.3 Example 2680 630 9.4 11.1 Example 3 580 250 9 12 Comparative 330 280 9.8 14Example 1 Example 4 525 520 9.5 11.4 Comparative 230 220 9.8 12.4Example 2EvaluationAdhesive Strength

Using each anisotropically electroconductive adhesive film (width 2 mm)of Examples and Comparative Examples described above, a plastic liquidcrystal panel with a pitch of 200 μm and a flexible printed board werecompression bonded under the conditions shown in Table 2, resulting in asample for evaluating the adhesive strength.

The flexible printed board herein used was a so-called two-layerflexible printed board in which no adhesive layer was present betweenthe base made of polyimide and the conductor made of copper. As theconductor, the one with a thickness of 12 μm was used.

Then, measurements were carried out for the adhesive strengths ofinitial state immediately after thermo compression bonding, and afterconducting a wet-heat resistance reliability test under the conditionsof a temperature of 60° C., a relative humidity of 95%, and for 500hours, respectively. The results are shown in Table 2.

Continuity Resistance

Using an ITO substrate not subjected to etching, a flexible printedboard, and each anisotropically electroconductive adhesive film,measurements were carried out for the continuity resistances of initialstate immediately after thermo compression boding and after the wet-heatresistance reliability test in accordance with the four-terminal method(JIS C 5012). The results are shown in Table 2.

As shown in Table 2, for the anisotropically electroconductive adhesivefilms of Examples 1 to 4, good results were obtained in all of adhesionstrength and continuity resistance.

On the other hand, for the anisotropically electroconductive adhesivefilm containing no epoxy acrylate of Comparative Example 1, and the onecontaining no phosphoric acid component of Comparative Example 2, theadhesive strengths were not good.

Peelability of Peeling Sheet

On the other hand, the anisotropically electroconductive adhesive filmsof Example 1 described above were formed on a peeling sheet obtained bycoating a silicone resin on a PET film, and a peeling sheet made ofPTFE, respectively.

Then, a sample plate was stuck through an adhesive tape on the surfaceof each anisotropically electroconductive adhesive film, resulting in asample for evaluating the peelability. For each sample for evaluatingthe peelability, the peeling sheet was pulled off in a direction atright angles thereto to determine the strength per 5-cm width as thepeel force. In this case, measurements were carried out for the peelforce (initial peel force) immediately after thermo compression bonding,and the peel force after allowing the sample to stand for 1 month underthe condition of a temperature of 23° C. (ordinary temperature). Theresults are shown in Table 3.

Further, for each sample for evaluating the peelability, measurementswere carried out for the adhesive strength immediately after thermocompression bonding, and the adhesive strength after allowing the sampleto stand for 1 month under the condition of a temperature of 23° C. Theresults are shown in Table 3.

TABLE 3 Peelability and adhesive strength according to the peeling sheettype Peel force (gf/5 cm) Adhesive strength (gf/cm) 23° C. after 23° C.after Initial 1 month Initial 1 month PTFE 30~40 30~40 865 855 PETsilicone 20~30 150~200 780 310 peeling treatment

As shown in Table 3, for the one using the peeling sheet made of PTFE,good results were obtained in peelability and adhesive strength.

On the other hand, for the one using a peeling sheet obtained by coatinga silicone resin on a PET film, the peel force increased, and the sheetbecomes difficult to peel and the adhesive strength was also reduced,after a lapse of about one month at ordinary temperature.

It is conceivable that this is attributable to the following fact. Thatis, the silicone slightly transfers to the surface of the adhesivebecause of the high affinity between silicone and the adhesivecomponent, resulting in deterioration in characteristics such asadhesive strength and moisture resistance.

As described above, the present invention can provide an insulatingadhesive film and an anisotropically electroconductive adhesive filmwhich satisfy requirements of low-temperature curability, high adhesion,and high reliability.

While there has been described what are at present considered to bepreferred embodiments of the present invention, it will be understoodthat various modifications may be made thereto, and it is intended thatthe appended claims cover all such modifications as fall within the truespirit and scope of the invention.

1. A low-temperature setting adhesive comprising a cured product of: anepoxy acrylate represented by the following formula:

wherein n is from 0 to 20; a resin component having no unsaturateddouble bond; a bis(methacryloyloxyethyl) hydrogen phosphate; and aradical polymerization initiator, the low-temperature setting adhesivefurther comprising a phosphate-based coupling agent made ofisopropyltris(dioctylpyrophosphate) titanate, wherein the epoxy acrylateis present in the amount of 15-85% by weight of adhesive, the resincomponent having no unsaturated double bond is present in the amount of30 to 90% by weight of the adhesive, and the bis(methacryloyloxyethyl)hydrogen phosphate is present in the amount of 0.01 to 20% by weight ofthe adhesive.
 2. The low-temperature setting adhesive according to claim1, wherein said bis(methacryloyloxyethyl)hydrogen phosphate componenthas a radical polymerizable reactive group.
 3. An anisotropicallyelectroconductive adhesive, comprising: a low-temperature settingadhesive, comprising as main components: a cured product of a bisphenolA epoxy acrylate having an acryloyl group at the terminal position; aresin component having no unsaturated double bond, abis(methacryloyloxyethyl)hydrogen phosphate, a radical polymerizationinitiator; and an electroconductive particle being dispersed in saidlow-temperature setting adhesive, the low-temperature setting adhesivefurther comprising a phosphate-based coupling agent made ofisopropyltris(dioctylpyrophosphate) titanate, wherein the epoxy acrylateis present in the amount of 15-85% by weight of adhesive, the resincomponent having no unsaturated double bond is present in the amount of30 to 90% by weight of the adhesive, and thebis(methacryloyloxyethyl)hydrogen phosphate is present in the amount of0.01 to 20% by weight of the adhesive.
 4. The anisotropicallyelectroconductive adhesive according to claim 3, wherein saidbis(methacryloyloxyethyl)hydrogen phosphate component has a radicalpolymerizable reactive group.
 5. The anisotropically electroconductiveadhesive according to claim 3, wherein said electroconductive particlecomprises a resin particle which is deformed when applied with pressureas a nucleus, and an electroconductive metal thin layer provided on asurface layer portion thereof.
 6. The anisotropically electroconductiveadhesive according to claim 4, wherein said electroconductive particlecomprises a resin particle which is deformed when applied with pressureas a nucleus, and an electroconductive metal thin layer provided on asurface layer portion thereof.
 7. The low-temperature setting adhesiveaccording to claim 1, wherein the resin component having no unsaturateddouble bond is present in the amount of 30-80% by weight of theadhesive.
 8. The anisotropically electroconductive adhesive according toclaim 3, wherein the resin component having no unsaturated double bondis present in the amount of 30-80% by weight of the adhesive.